linux-kernel - Re: [PATCH v1] lib/hashtable_test.c: add test for the hashtable structure

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Date:   Fri, 13 Jan 2023 14:45:29 -0800
From:   Daniel Latypov <dlatypov@...gle.com>
To:     Rae Moar <rmoar@...gle.com>
Cc:     brendanhiggins@...gle.com, davidgow@...gle.com,
        skhan@...uxfoundation.org, kunit-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v1] lib/hashtable_test.c: add test for the hashtable structure

On Fri, Jan 13, 2023 at 2:23 PM Rae Moar <rmoar@...gle.com> wrote:

<snip>

> > Note: given x is supposed to point to a or b, I don't know if checking
> > against a.data does us much good.
> > If we're trying to check that hash_add() doesn't mutate the keys and
> > data, this code won't catch it.
> > We'd have to instead do something like
> >   if(x->key != 1 && x->key != 2) KUNIT_FAIL(test, ...);
> >
>
> This seems like a good change to me in combination with changing it to
> x->visited++;.
> Although David's suggestion might be slightly more exhaustive.
> Why wouldn't it be important to check that the key matches the data?

Checks like
  KUNIT_EXPECT_EQ(test, x->data, a.data);
won't do anything, given that x == &a.
We're just comparing x->data to itself.

So we would have to write something instead like
  hash_for_each(hash, bkt, x, node) {
          x->visited++;
          if (x->key == a.key) {
                  KUNIT_EXPECT_EQ(test, x->data, 13);
          } else if (x->key == b.key) {
                  KUNIT_EXPECT_EQ(test, x->data, 10);
          } else { /* some call to KUNIT_FAIL about a bad key */ }
  }

Maybe that's worth it in one of the test cases, but I don't know if
it's necessary to replicate this in the other places where we're
incrementing `visited` by checking keys.

Daniel